ZOOLOGY AND BOTAN, MICROSCOPY, ETC. 



Ill 



distribute the air after it escapes ; and this is also facilitated by tilting 

 the end of the tube R to 23' from the horizontal. 



Schweizer's Reagent.*— G. B. de Toni has discovered a way of 

 making this reagent, which obviates the tiresome task of repeatedly 

 washing the copper hydroxide, and thus simplifies the preparation: 

 10 gnu. of pure crystallised sulphate of copper are reduced to a fine 

 powder in a mortar. While grinding, 2 grm. of powdered caustic soda 

 are added a little at a time : from time to time a few drops of distilled 

 water are allowed to fall on the mixture. To the resulting greenish 



R 



Fig. 17. 



mass are added gradually, and stirring the while, 25—40 c.cm. of strong 

 ammonia (26-29 Baume), which dissolves the hydroxide of copper 

 formed by the action of the soda on the copper sulphate. The mixture 

 is then filtered through glass wool : the filtrate of a dark blue colour 

 has all the properties of Schweizer's reagent. Cotton, when treated 

 with this fluid, is completely dissolved, and when the cupro-ammoniacal 

 solution is treated with water, or better with acidulated water, cellulos< 

 is precipitated in fine white flakes. - •■- 



Another method of preparing the reagent is given by the author : 

 10 grm. of copper sulphate are dissolved in 200 c.cm. of distilled water 

 and mixed with 7 grm. of barium hydroxide dissolved in 200 c.cm. of 

 water. The precipitate which forms is filtered off on glass wool, and 



* Atti K. Istit. Veneto, lxv. (1905-6) pp. 593-6. 



